1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to gamut mapping, and more specifically to performing a gamut compression and extension adaptively to a color gamut of an imaging source device, and the configuration of the color gamut of a target device.
2. Description of the Related Art
Gamut compression is the process of mapping colors that do not exist within the color gamut of a target device among original images of a source device, i.e., the target color gamut, into the color gamut of the target device, especially in a case where the color gamut of the target device is larger than the color gamut of the source device during the color reproduction process between apparatuses.
In general, color input/output devices for reproducing colors, e.g., monitors, scanners, cameras, printers, etc., use different color spaces or color models by application fields. In case of a color image, for example, a printing device uses the CMY color space, color Cathode Ray Tube (CRT) motors or computer graphic devices use the RGB color space, and devices dealing with hue, chroma and brightness use the HSI color space. Also, there is the CIE color space for defining device-independent colors that can be accurately reproduced in any device. Typical examples of the CIE color space include a CIE-XYZ, CIE-Lab, and CIE-Luv.
Besides the color space, color input/output devices have different ranges of color (i.e., a color gamut) that can actually exist within any color model for the devices. The difference in the color gamut explains why the same image looks different in every input/output device. Therefore, if differences in color gamuts between an input color signal and a device for reproducing the input color signal are great, the input color signal should be adequately converted to match the different color gamuts and enhance color reproducibility (this process is called gamut mapping).
Usually, for gamut mapping between different color input/output devices, a Gamut Boundary Description (GBD) of a given source device and a target device is first prepared. After converting the color space of an input color signal, the gamut mapping process is performed on lightness and chroma without changing hue.
In detail, a DDCS (Device Dependent Color Space) color space such as RGB and CMYK of the input color signal is converted to a DICS (Device Independent Color Space) such as CIE-XYZ and CIE-Lab, and the DDCS is converted again to the coordinates LCH (Lightness, Chroma, Hue). Then, on a plane with uniform color, namely, an LC plane, the gamut mapping process is performed on the lightness and chroma. One thing necessary before performing the gamut mapping is to learn the DICS or the color gamut of a device in LCH.
If the color gamut of a source device is broader than the color gamut of a target device, an original image of the source device should be mapped into the color gamut of the target device by using the prepared GBD. In other words, the original image of the source device being outside of the target device should be mapped into the color gamut of the target device, so that the target device can reproduce colors.
However, during the gamut compression process for compressing the colors of the original image of the source device within the color gamut of the target device, the colors of the original image are sometimes compressed too excessively. This occurs because the same method is applied to every color. In addition, although the related art gamut mapping technique is more focused on matching colors in the target device to the original image of the source device, users tend to make much of their color preference more than the accuracy of color matching. Therefore, an adaptive gamut compression process needs to be performed in consideration of the color gamut of the source device and the configuration and size of the color gamut of the target device.
Moreover, in order to increase the user's preference for particular original images of the source device, it is necessary to extend the compressed colors of the image. Especially, gamut extension should be done to increase appropriate chroma, under the restriction that a user's memory colors such as the color of skin, the color of the sky, and the color of field are not affected. Also, chroma extension is needed to provide high quality images after performing the gamut compression process on high chroma images.